This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the
pathway.
If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.

Organisms produce hydrocarbons of different types by different mechanisms. Several mechanisms have been described for the production of hydrocarbons from fatty acids or their intermediates, including synthesis of alkanes from fatty aldehydes by decarbonylation (see alkane biosynthesis I and alkane biosynthesis II), synthesis of long-chain olefins by head-to head condensation of fatty acids (this pathway), and production of alkenes from fatty acids by decarboxylation (see terminal olefins biosynthesis I and terminal olefins biosynthesis II).

This class of hydrocarbons have been shown by carbon-14 labeling studies to derive from fatty acids [Albro69]. The process by which these olefins are synthesized, which was described in 1929 [Channon29], is known as head-to-head hydrocarbon biosynthesis and involves the coupling of the head (C1) and the α-carbon (C2) of two fatty acids in a reaction that involves decarboxylation of one of the fatty acid carboxyl groups [Albro69a, Albro69b].

While the major products of the enzyme are olefins, the enzyme also produces ketones as minor products. The authors speculate that the enzyme can catalyze both decarboxilative and nondecarboxylative acyl group condensations. The nondecarboxylative condensation produces a 3-oxo acid intermediate that will decarboxylate spontaneously into a ketone [Sukovich10].

Another study of the pathway, which was conducted with Micrococcus luteus NCTC 2665 proteins, concluded that the pathway is somewhat different, and that the substrates for OleA are one fatty acyl-CoA and one β-ketoacyl-CoA, since purified OleA protein incubated with a fatty acyl-CoA substrate alone could not catalyze the reaction without addition of Escherichia coli cell lysate. The authors speculate that additional enzymes in the lysate are necessary for conversion of some of the substrate to a β-ketoacyl-CoA form [Beller10].